Propionate serves as a degradable control agent of citrus canker by acidifying cytoplasm and depleting intracellular ATP in <i>Xanthomonas citri</i>

Citrus canker, caused by <i>Xanthomonas citri</i> subsp. <i>citri</i> (Xcc), poses a substantial threat to global citrus production. Current disease control relies on the widespread application of copper-based bactericides. However, the excessive and recurrent use of copper has resulted in adverse outcomes, such as the emergence of copper-resistant strains and detrimental impacts on both the environment and human health. In this study, we demonstrate that propionate effectively inhibits the growth of <i>Xanthomonas citri</i> and is degradable by soil microbes, making it a promising and economic alternative for citrus canker management. Propionate exerts pleiotropic effects on Xcc by disrupting membrane potential, motility, and the type III secretion system. It acts as a bacteriostatic agent by acidifying the bacterial cytoplasm and disrupting proton homeostasis, which depletes intracellular ATP and induces cell dormancy. Through a Tn5 mutant library screen, we identified a propionate-sensitive mutant with a disrupted <i>prpC</i> gene, part of the <i>prp</i> operon, which is involved in propionate metabolism and regulated by PrpR. PrpR represses the <i>prp</i> operon by binding to a palindromic motif in the <i>prpB</i> promoter region. Our findings highlight propionate as a favorable control agent for citrus bacterial canker, offering effective disease management while mitigating the environmental and health concerns associated with copper-based treatments.IMPORTANCECitrus canker severely impacts citrus production, threatening a major fruit industry. Traditionally, managing this disease has depended on copper-based bactericides, which bring significant downsides, including copper resistance in pathogens and environmental toxicity. This study identifies propionate as a promising alternative to copper treatments for combating citrus canker caused by <i>Xanthomonas citri</i> subsp. <i>citri</i>. Propionate offers a dual benefit: it disrupts essential bacterial functions, effectively controlling the pathogen, and it is biodegradable in soil, which reduces environmental impact. Our findings show that propionate acidifies cytoplasm and disrupts critical bacterial processes such as membrane potential and motility, while depleting intracellular ATP and inducing cell dormancy. Propionate, therefore, emerges as an eco-friendly, cost-effective option for sustainable management of citrus bacterial canker, addressing both agricultural and environmental challenges in citrus production.